Position sensors having a permanent magnet and a hall element sensitive to magnetism for outputting signals are widely known in the art. However, linearity of an output of the position sensor of this kind with respect to displacement is basically insufficient, and the position sensors of this kind are generally expensive. Therefore, an application of the position sensors of this kind has to be restricted. In order to solve the above-mentioned problems, Japanese Patent Laid-Open No. 2003-83764 discloses a position sensor comprising a hollow detection coil to which constant current of a prescribed frequency and amplitude is applied, and a metal body inserted into the detection coil. According to the teachings of Japanese Patent Laid-Open No. 2003-83764, a change in impedance according to insertion amount of the metal body is detected by detecting voltage at both ends of the detection coil, and the detected voltage is converted into a position signal representing positional information. Therefore, the position sensor taught by Japanese Patent Laid-Open No. 2003-83764 is capable of detecting an amount of displacement of the metal body and a velocity of the displacement on the basis of the detected voltage. In addition, Japanese Patent Laid-Open No. 2003-83764 discloses different kinds of examples such as an example in which the detection coil and the metal body are formed linearly, and an example in which the detection coil and the metal body are curved with a predetermined curvature. According to the latter example, the curved metal body is rotated around a center of curvature by stepping an accelerator pedal thereby varying an insertion amount of the metal body in the curved detection coil.
As described, a trunnion of a toroidal type transmission is a well known member performing a translational motion. In this connection, Japanese Patent Laid-Open No. 07-317867 discloses a device, which is adapted to detect an rotation angle and a displacement amount of a trunnion by a sensor through a movement of a precess cam. According to the teachings of Japanese Patent Laid-Open No. 07-317867, specifically, the sensor is contacted with a spiral cam face of the precess cam to detect a synthesized value of the rotation angle and a displacement of the trunnion, for the purpose of controlling a speed change ratio.
On the other hand, Japanese Patent Laid-Open No. 2002-195393 discloses a device comprising two kinds of sensors such as a sensor for detecting an oscillation angle of the trunnion and a sensor for detecting an amount of displacement of the trunnion. That is, Japanese Patent Laid-Open No. 2002-195393 discloses an invention for controlling a speed change ratio of a toroidal type continuously variable transmission by detecting an amount of displacement and a (tilted) rotational angle of the trunnion. According to the teachings of Japanese Patent Laid-Open No. 2002-195393, a contact sensor as well as a noncontact type sensor including a capacitance sensor and an optical sensor can be used to detect the aforementioned amount of displacement and the rotational angle.
The position sensor taught by Japanese Patent Laid-Open No. 2003-83764 is capable of detecting a position of a member moving linearly and a movement of a member rotating around a predetermined fulcrum point such as an accelerator pedal, by detecting a migration of the metal body with respect to the detection coil, that is, by detecting a change in the impedance. However, in order to detect a translational movement of a member, two position sensors are required to detect a rotation and a linear movement of the member. Therefore, comparatively large space is required for arranging two sensors on the member performing the translational movement and this restricts an application thereof. For example, in case the toroidal type continuously variable transmission, a space around the trunnion thereof is limited, and a plurality of power rollers and trunnons supporting the power rollers are arranged on one variator (or a cavity). Therefore, a number of position sensors are required for detecting an amount of displacement and a tilted rotational angle of the trunnion. Thus, it is difficult to use the position sensor taught by Japanese Patent Laid-Open No. 2003-83764 in the toroidal type continuously variable transmission.
In addition to the above-mentioned disadvantage, according to the position sensor taught by Japanese Patent Laid-Open No. 2003-83764, the metal body moving within the detection coil has to be connected with an object to be detected. Thus, the position sensor of Japanese Patent Laid-Open No. 2003-83764 is not easy to be assembled. Moreover, in case the object to be detected is a member performing a complex movement while rotating such as the trunnion, detection accuracy may be degraded by such complex movement of a portion to be detected. Therefore, it is necessary to further analyze a detection result.
As described, the device taught by Japanese Patent Laid-Open No. 07-317867 requires the precess cam. This means that the device taught by Japanese Patent Laid-Open No. 07-317867 cannot be applied to an apparatus which is not provided with the precess cam. Moreover, according to the device taught by Japanese Patent Laid-Open No. 07-317867, a load is applied to one sensor in a rotational direction as well as in an axial direction. For this reason, detection accuracy may be degraded by a frictional resistance at a contact portion.
As also described, the device taught by Japanese Patent Laid-Open No. 2002-195393 requires both of the sensor for detecting rotation and the sensor for detecting a linear displacement. That is, the device taught by Japanese Patent Laid-Open No. 2002-195393 also contains the aforementioned disadvantage of the position sensor taught by Japanese Patent Laid-Open No. 2003-83764.
In addition, the noncontact type sensor as disclosed in Japanese Patent Laid-Open No. 2002-195393 is adapted to detect a displacement by detecting a change in a capacitance or a laser light in response to a migration of a portion of the trunnion or a migration of a member to be detected arranged on the trunnion. That is, it is necessary for the object such as the trunnion to be provided with a member to be detected. For this purpose, the member to be detected has to be arranged on a moving portion side, and the sensor has to be arranged on a fixed portion side. Thus, the device of Japanese Patent Laid-Open No. 2002-195393 cannot be assembled easily, and therefore an easiness of assembly has to be improved. On the other hand, in case of using the contact sensor, the contact sensor has to be connected with an object to be detected. That is, the contact sensor also has to be connected with both moving portion and the fixed portion. Thus, an easiness of assembly also has to be improved even in case of using the contact sensor. In this case, especially, if the object to be detected is a member performing a complex movement while rotating such as the trunnion, detection accuracy may be degraded by such complex movement of the portion to be detected. Therefore, it is necessary to further analyze a detection result.